Pope Emeritus Benedict XVI, right, hugs Pope Francis in St. Peter's Basilica during the ceremony marking the start of the Holy Year, at the Vatican, Tuesday, Dec. 8, 2015. Pope Francis declared Tuesday that mercy trumps moralizing in the Catholic Church, as he opened a special Holy Year marked by unprecedented security aimed at thwarting a Paris-style attack at the Vatican. (AP Photo/Gregorio Borgia)

Pope Francis, center, kisses the altar as he celebrates Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. Francis launched the 12-month jubilee to emphasize what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Alesssandra Tarantino)

Pope Francis, center, kisses the altar as he celebrates Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015.

Pope Francis, center, celebrates Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. Francis launched the 12-month jubilee to emphasize what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Andrew Medichini)

Pope Francis, center, celebrates Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. Francis launched the

A woman holds up French flag as she waits in St. Peter's Square for the start of a Mass celebrated by Pope Francis on the occasion the opening of the Holy Door of St. Peter's Basilica, at the Vatican, Tuesday, Dec. 8, 2015. Francis on Tuesday pushes open the huge bronze Holy Door to formally launch his yearlong "revolution of tenderness" amid unprecedented security aimed at thwarting the threat of a Paris-style attack at the Vatican. (AP Photo/Gregorio Borgia)

A woman holds up French flag as she waits in St. Peter's Square for the start of a Mass celebrated by Pope Francis on the occasion the opening of the Holy Door of St. Peter's Basilica, at the Vatican, Tuesday,

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Gregorio Borgia)

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of

Faithful and pilgrims wait to enter in St. Peter's Square for the start of a Mass celebrated by Pope Francis on the occasion the opening of the Holy Door of St. Peter's Basilica, which formally starts the Jubilee of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. (AP Photo/Alessandra Tarantino)

Faithful and pilgrims wait to enter in St. Peter's Square for the start of a Mass celebrated by Pope Francis on the occasion the opening of the Holy Door of St. Peter's Basilica, which formally starts the

Pope Francis spreads incense during a Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. Francis launched the 12-month jubilee to emphasize what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Gregorio Borgia)

Pope Francis spreads incense during a Mass ahead of the opening of the Holy Door of St. Peter's Basilica, formally starting the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. Francis launched the

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Andrew Medichini)

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of his papacy: to show the merciful and welcoming side of a Catholic Church more often known for its moralizing and judgment. (AP Photo/Gregorio Borgia)

Pope Francis pushes open the Holy Door of St. Peter's Basilica, formally launching the Holy Year of Mercy, at the Vatican, Tuesday, Dec. 8, 2015. The 12-month jubilee emphasizes what has become the leitmotif of

VATICAN CITY (AP) -- Pope Francis pushed open the great bronze doors of St. Peter's Basilica on Tuesday to launch his Holy Year of Mercy, declaring that mercy trumps moralizing in his Catholic Church.

Francis stood in prayer on the threshold of the basilica's Holy Door then walked through it, the first of an estimated 10 million faithful who will pass through over the course of the next year in a rite of pilgrimage dating back centuries.

A thin and frail Emeritus Pope Benedict XVI walked through the doorway right after Francis, gingerly negotiating the two steps with the help of a cane and his longtime assistant. It was a rare outing for the 88-year-old Benedict, whose historic resignation led to Francis' election and a papacy dedicated to showing the merciful side of the church.

Some 5,000 extra police, carabinieri and soldiers have been deployed around Rome, and a no-fly zone imposed on its skies, to protect the pilgrims who are flocking to Rome on foot, by car, train and plane to participate in the yearlong celebration.

Security was heightened after the Vatican was listed as a possible target following the Paris attacks, but the extra police patrols and traffic stops extended far beyond the immediate vicinity of the Vatican or even the other main pilgrimage sites in Rome.

Francis launched the 12-month jubilee to emphasize what has become the leitmotif of his papacy: showing the merciful and welcoming side of a Catholic Church more often known for moralizing and casting judgment.

"How much wrong we do to God and his grace when we speak of sins being punished by his judgment before we speak of their being forgiven by his mercy," Francis told an estimated 50,000 people gathered under rainy skies for his Mass opening the jubilee. "We have to put mercy before judgment, and in any event God's judgment will always be in the light of his mercy."

The Vatican's Holy Door, located to the right of the basilica's main entrance, is decorated with 16 bronze panels depicting the redemption of man's sin through mercy. Passing through it is meant to symbolize the pilgrimage of life's journey and the sacrifices endured.

"We have to absorb the message that God always forgives us, which is the message that the pope gives to us," said Maria Sila, a pilgrim from Buenos Aires as she waited for the Mass to begin.

After Francis and Benedict walked through the doorway, the first throngs of pilgrims followed suit, led off by the Italian president and other dignitaries.

In a sign that Francis himself was taken aback by Benedict's frailty when he saw him at the Holy Door, he asked the throngs of pilgrims in the piazza to send their prayers for his "good health." The crowd responded with cheers and applause.

Holy Years are generally celebrated every 25-50 years, and over the centuries they have been used to encourage the faithful to make pilgrimages to Rome to obtain an "indulgence" -- the ancient church tradition related to the forgiveness of sins that roughly amounts to a "get out of Purgatory free" card.

Unlike in Martin Luther's time, these Holy Year indulgences are free and available to those who pass through the Holy Door.

The last jubilee was in 2000, when St. John Paul II ushered in the church's third millennium and some 25 million pilgrims flocked to a Rome that had undergone a multimillion-dollar facelift for the occasion.

In typical Francis fashion, the pope made clear from the start that he wanted this Holy Year to be a more sober occasion. For the first time, the pope instructed all cathedrals around the world to open their Holy Doors to pilgrims to encourage the faithful to mark the jubilee at home rather than coming to Rome.

Nevertheless, Italian officials seized on the excuse of the jubilee to allocate millions of euros for dozens of public works projects around the capital, practically none of which has been completed.

Francis announced his Holy Year on the second anniversary of his papacy, saying his aim was "to give comfort to every man and every woman of our time." It was in keeping with his priority to make the church a "field hospital" for injured souls, where the wounded are welcomed and loved, not judged.

The jubilee year will feature a host of special Masses and extra general audiences to accommodate the throngs of pilgrims, while Francis himself has set aside one Friday each month to slip out of the Vatican to perform an act of mercy himself, in private.

For all the pomp of Tuesday's ceremony, Francis technically launched the Holy Year of Mercy last week in Central African Republic, when he pushed open the Holy Door of the Bangui cathedral. His aim was to give the conflict-weary Christians there a spiritual boost, and show the universality of his message of mercy.

Elsewhere around the world, Holy Doors will be opening at cathedrals starting this Sunday.

On Tuesday night, the Vatican will lend itself to another one of Francis' preoccupations -- environmental protection. A coalition of humanitarian groups has banded together to screen images of nature by well-known photographers and filmmakers on the facade of St. Peter's.